1. Field of the Invention
The present general inventive concept relates to a hard disk drive (HDD), and more particularly, to a head gimbal assembly (HGA) of a HDD having a support structure disposed between a slider with a magnetic head and a supporting flexure.
2. Description of the Related Art
A hard disk drive (HDD) is a well-known information storage device that records data on a disk and/or reproduces data from the disk using a magnetic head. The HDD includes an actuator which moves the magnetic head to a desired position on the disk. The actuator includes a swing arm, a voice coil motor (VCM), and a head gimbal assembly (HGA). The swing arm is pivotally installed on a base member of the HDD. The VCM provides a driving force to pivot the swing arm. The HGA is installed at the swing arm to support the magnetic head so as to elastically bias the magnetic head toward a surface of the disk.
FIG. 1A is a perspective view of a HGA of a conventional HDD, and FIG. 1B is an enlarged view of portion A of FIG. 1A. Referring to FIGS. 1A and 1B, an HGA 10 of an actuator of a HDD includes a flexure 12, a slider 14, and a magnetic head 16. The slider 14 is attached to and supported by the flexure 12. The magnetic head 16 is disposed in the slider 14. A plurality of traces 18 are provided on the flexure 12 and are electrically connected to the magnetic head 16. A plurality of pads 20 are provided at a side of the slider 14. The traces 18 are bonded to the pads 20 through solder balls 22 so as to be electrically connected to the pads 20. The number of traces 18 is typically four (4) corresponding to two read signals R+ and R− and two write signals W+ and W−. Accordingly, the number of the pads 20 is typically four (4) as well.
Various modifications have been recently applied to the HGA to support additional features and to facilitate its construction. For example, flying on demand (FOD) is a technique to thermally expand the slider 14 through an application of heat thereto, which consequently reduces a gap between the magnetic head 16 and the surface of the disk, i.e., to dynamically lower a flight height of the magnetic head 16. Thus, two additional traces 18 corresponding to two FOD signals FOD+ and FOD− and two additional pads 20 are required to apply such a FOD technique. Thus, the total number of traces 18 provided on the flexure would be six (6), and the number of pads 20 provided at the slider 14 would also be six (6) to implement an HGA with FOD support.
Other recent modifications include forming a slot 24 in the flexure 12, such as is illustrated in FIG. 1B, to verify proper alignment of the slider 14 during assembly of the HGA. As is illustrated in FIG. 1B, the slot 24 may be formed as an arc defining an island 13 adjacent the circuit pad edge of the slider 14. Such a slot 24 can be used to assure alignment of the slider 14.
The implementation of a greater number of additional features on an increasingly smaller HGA is limited by the physical support structure that allows the magnetic head 16 to fly above the disk at its proper height. The support structure is also required to prevent discontinuities from forming between the pads 20 of the magnetic head 16 and the corresponding traces 18, particularly after physical shock has been applied to the HDD. Consider, for example, when the number of pads 20 provided on the slider 14 is increased while the size of each pad 20 is required to remain fixed. Under such conditions, the distances between the pads 20 are reduced and the sizes of the solder balls 22 must also be reduced. As a result, the mechanical support provided by the solder bond between the pads 20 and the traces 18 is significantly lowered. It has been determined through measuring the bonding strength between the pads 20 and the traces 18 that the bonding strength is approximately 20% lower when the number of pads 20 is increased from four (4) to six (6). Further compromises to the support structure are introduced by the slot 24, which creates a point where non-elastic deformation of the flexure 12, e.g., a bend, may occur. Although some bending of the flexure 12 can be tolerated if significant degradation of the flight characteristics of the slider 14 is avoided, most non-elastic deformation of the flexure 12 renders the HGA unusable.
If the HGA 10 having the above-described structure undergoes shock from an outside source, the flexure 12 may strike against a ramp (not illustrated) on which the HGA 10 is parked. If the bonds between the pads 20 and the traces 18 have diminished bonding strength and the slot 24 is formed in the flexure 12, a front end of the flexure 12 may be non-elastically deformed. Not only can the flight characteristics of the slider 14 be compromised as a result of such an impact, but also the electrical circuit between the pads 20 and the traces 18 may open to render the HGA 10 inoperative.
FIGS. 2A, 2B, and 2C are photographs illustrating problems of the HGA 10.
FIG. 2A illustrates a deformation of the flexure 12 caused by the impact of the flexure 12 against the ramp. Lighter regions depicted in FIG. 2A signify a portion of the flexure 12 that has been significantly deformed. As is illustrated in FIG. 2B, the front end of the flexure 12 has been non-elastically deformed to a great degree.
Referring to FIG. 2C, not only is the front end of the flexure 12 bent but the bonding parts between the pads 20 of the slider 14 and the traces 18 are cracked.
FIG. 3 is a cross-sectional view of the flexure 12 taken along line B-B′ of FIG. 1B, and FIG. 4 is a photograph illustrating the cracked solder bonds between the pad 20 at an edge of the slider 14 and the trace 18.
Referring to FIGS. 1B and 3, the flexure 12 may have a base structure formed of a stainless sheet. A dielectric film 17 formed of polyimide is applied to a surface of the flexure 12, and the traces 18 are formed of copper (Cu) on the dielectric film 17. A portion 13 of the flexure 12 is contained within the boundaries of the slot 24 forms an island shape in the flexure 12 that is isolated from other parts of the flexure 12 by the slot 24. Consequently, those traces 18 positioned at the outer edges of the slider 14 are not supported by the flexure 12 formed of the stainless sheet. Thus, if the HDD suffers an impact from an outside force, it is highly likely that the bonding parts between the traces 18 at the edges of the flexure 12 and the corresponding pads 20 will be cracked, especially if the HGA 10 is parked on the ramp 140.
Referring to FIG. 4, the solder bond between the pad 20 positioned at the edge of the slider 14 and the trace 18 corresponding thereto is cracked.
As described above, in current HGA design trends, the strength of the support structure stabilizing the fight of the slider and the electrical contact between pads and traces is lowered.